Field of the Invention
The present invention relates to a device for holding a turbine engine blade for the purposes of machining.
Description of the Related Art
A turbine engine blade comprises an airfoil that is to be placed in a gas-flow passage, and a root that is to be engaged in a slot in a disk. The airfoil and the root are separated by a platform defining a portion of the inside wall of the gas-flow passage.
When fabricating a blade, it is conventional to use forging or casting to make an un-finished part having dimensions that correspond to the finished dimensions, so far as the airfoil-forming portions is concerned. In contrast, the portion that is to form the root is no more than a blank that needs to be machined in order to give it its final shape and dimensions.
Once machined, the blade root still has projecting edges of angles that need to be rounded or smoothed during an operation referred to as fitting or radiusing.
A blade root is generally radiused manually by an operator who machines the projecting edges using a carbide bur or a brush, for example. Since that radiusing operation is manual, dimensional differences can appear from one blade to another or from one operator to another.
If the radiusing of a blade root is performed in insufficient or inaccurate manner (e.g. because the projecting edge is not sufficiently rounded), fabrication operations further downstream may suffer. This happens in particular when shot blasting a poorly-radiused blade root, since some of the beads of shot can be deformed by an edge that projects too much. A projecting edge also gives rise to stress concentrations that lead to premature cracking of the blade root.
Dimensional differences between the blade roots can also complicate assembling the roots in the slots of disks.
Finally, manual radiusing operations are complex and expensive.
Patent application FR 10/57384, in the name of the applicant and not yet published, discloses a method of radiusing blade roots with the help of a numerically-controlled machine. While they are being radiused, the blades are held in tooling comprising a support having housings formed therein. The airfoil of the blade is clamped between two jaws that are hinged together at one end and fastened together at the other end with the help of a first screw. The jaws have presser studs for pressing against the blade. Once the blade is in place between the jaws, a second screw provided on one of the jaws serves to press the blade against the above-mentioned presser points. The jaws and the blade are then mounted in a housing of the support and they are held therein with the help of latches.
A plurality of blades can thus be mounted simultaneously on the support of the tooling in different housings, in order to be subjected to radiusing.
Nevertheless, installing and removing the blades is time-consuming. Specifically, after radiusing, for example, when it is desired to remove a blade, it is necessary to move the latches, to withdraw the jaws together with the blade from the housing in the support, and to unscrew the second screw in order to be able to withdraw the airfoil from the jaws.
Also, such a mounting does not make it possible to know accurately the position of the blade relative to the support. Specifically, the jaws are mounted in the housing of the support with a small amount of mounting clearance such that, even if the blade is correctly positioned on its presser points, it is not possible to know exactly the position of the jaws (and thus of the blade) relative to the support that constitutes a known frame of reference.